a. Field of the Invention
The present invention relates to a valve, and more particularly to a valve adapted for use in a high pressure pump, such as a poppet valve to receive flow from a high pressure piston.
b. Background Art
High pressure pumps are utilized in a variety of applications. In such pumps a fluid is brought to pressures as high as 10,000 psi or even as high as 100,000 psi or greater. This pressurized fluid, (generally water) can then be discharged through a nozzle as a high velocity stream of water to accomplish functions such as cutting, abrading, etc. A common arrangement of such a high pressure pump is to have a plunger or piston which reciprocates in a cylinder on an intake stroke where the plunger retracts to draw water into the cylinder chamber, and a discharge stroke where the plunger acts against the water to discharge it at a very high pressure.
An outlet valve is positioned at the end of the cylinder to receive the flow of high pressure fluid. On the pressure stroke, the outlet valve opens to receive the flow of high pressure fluid, while on the return stroke of the plunger, the outlet valve closes to prevent the pressurized fluid from returning into the cylinder with water flowing into the cylinder through an inlet valve.
A typical valve used in this application is a poppet valve, where the valve element has a transversely extending contact surface which fits against a matching contact surface of the valve member to close the passageway leading from the high pressure chamber. A spring or other means is used to urge the valve element toward its closed position. On the pressure stroke of the plunger, the pressure in the cylinder chamber moves the valve element to its open position to permit the pressurized fluid to flow around the valve element to an accumulator or manifold to be utilized in some operation, such as forming a high velocity jet.
One of the problems associated with such poppet valves is that there is sometimes a delay in the proper opening of the valve, which is commonly described as "sticking" of the valve. Desirably, when the force resulting from pressure of the fluid within the cylinder chamber reaches a level just at or above the combined force of the pressure downstream of the poppet valve and of the biasing spring, the poppet valve should open so that there is a flow of fluid from the chamber to a down stream location without any substantial discontinuity in fluid pressure. However, if there is a delay in the proper opening of the valve, there can be a pressure spike where the pressure in the cylinder continues to rise to an undesirably high level. Even without such pressure surges, the fluid is pressurized to a very high level, thus imparting substantial loads on the components of the pump assembly. Thus, pressure surges above the desired level place rather severe stresses on the components of the pumping assembly.
Some of the prior art approaches for alleviating the problem of delay in opening of such poppet valves are based on the belief that the delay is caused by sealing over too large an area. To explain this further, if the area of the poppet element that is exposed to high pressure on the downstream side is greater than the area of the poppet element that is exposed directly to fluid pressure on the upstream side, it is assumed that the forces acting on the valve element will not balance until the pressure times the effective pressure area on the downstream side (plus the force of the biasing spring) is equal to the pressure times the effective pressure area on the upstream side. Thus, one prior art approach is to minimize this effect by roughening the contact surfaces to discourage full contact of the valve element with the short term solution since the contact forces tend to make the contact surfaces more smooth. Another prior art approach is to minimize the contact area between the valve element and the valve seat. However, this can undesirably increase the local load bearing forces (both static and impact) with a consequent increase in wear.